1. Field of the Invention
The present invention relates to a reflective liquid crystal display and, more particularly, to a reflective liquid crystal display which can enhance light efficiency.
2. Description of the Prior Art
Generally, a liquid crystal display ("LCD") is classified into a transmissive type and a reflective type: the former uses a backlight for radiating light frontward, while the latter uses a reflective film disposed on a rear side of the LCD to reflect light transmitted from a front side.
FIG. 4 shows a sectional view of a conventional reflective LCD.
A conventional LCD comprises upper and lower substrates 2A and 2B facing each other, ITO electrodes 4A and 4B formed on opposing inner surfaces of the upper and lower substrates 2A and 2B, respectively, and a liquid crystal layer 6 disposed between the upper and lower substrates 2A and 2B.
Attached on outer surfaces of the upper and lower substrates 2A and 2B are a polarizer 8 and a reflective layer 10, respectively.
In addition, a red R, green G and blue B color filter with a black matrix BM may further provided to realize a color display.
In the operation of the LCD, when electric field is generated between the upper and lower ITO electrodes 4A and 4B by applying driving signals, the orientation of liquid crystal molecules in the liquid crystal layer 6 changes in accordance with a direction of the electric field to selectively transmit light.
Describing the transmission of the light, outer incident light is changed from circular polarization into linear polarization while passing through the polarizer 8, and the linear polarization is changed into elliptical polarization while passing through the liquid crystal layer 6 via the upper substrate 2A, the RGB color filter, and the ITO electrode 4A. Then, the elliptical polarization passes through the ITO electrode 4B and the lower substrate 2B, then is reflected on the reflect layer 10.
The reflected light is projected through the polarizer 8 in reverse order of the light incident course, thereby displaying an image.
FIG. 5 shows a schematic diagram for illustrating changes in an amount of light passing through the elements of the conventional LCD.
When outer light is introduced into the polarizer 8, 50% of the light ("S-wave") is absorbed and disappeared by the polarizer, and 50% of the light ("P-wave") is transmitted to the reflective layer 10 via the liquid crystal layer 6, then reflected thereon to be projected to the outside.
That is, 50% of the light is disappeared in the polarizer 8. Therefore, the light efficiency of the LCD becomes about 50%. Light wave indicated by P' in the drawing is the P-wave directed to the outside.
As described above, since the light efficiency is low, the image to be displayed is not clear. Therefore, many methods have been proposed to solve the above-described problems.
One of the methods is to use a high transmissive polarizer, which is sold in the trademark of DEBF polarizer by 3M Company.
However, even if the high transmissive polarizer is used, there is limitation in improving the light efficiency.